An agricultural plant cutting machine, such as, but not limited to, a combine or a windrower, generally includes a header operable for severing and collecting or gathering plant or crop material as the machine is driven over a field. The header will have a plant cutting cutterbar for severing the plants or crops, which will typically comprise an elongate sickle mechanism sidewardly reciprocatingly movable relative to a non-reciprocating guard structure. On some headers, the cutterbar and guard structure are flexible, that is, capable of flexing upwardly and downwardly at locations along the width of the header, to facilitate operation while in contact with the ground along the width of the header, and while enabling conforming to and accommodating irregularities and unevenness in the ground surface.
Typically, a flexible cutterbar is supported at spaced locations along its length on forward ends of pivoting support arms having rear ends which pivotally connect to the header. The individual pivotability of the support arms enables the respective locations of the cutterbar to flex individually, downwardly and upwardly for conforming to or accommodating ground surface irregularities, and, if the header is equipped with an automatic height control system, for triggering operation of that system.
A ground contour following capability of a flexible cutterbar can be enhanced by exerting a preload force against it, for example, to reduce the amount of applied external force required to move the support arm and supported portion of the cutterbar upwardly. This is desirable and advantageous, as it can improve the cutterbar flex reaction to upwardly extending ground irregularities and increased firmness and hardness, resulting in smoother operation with less jarring. It can also act to limit the downward flexure of the cutterbar into ground depressions and the like.
In many instances, it is desirable for the cutterbar to be adjustably movable also in a fore and aft direction in relation to crop gathering and collecting apparatus such as a reel and an auger or draper belt of the header, for adapting to different crop varieties and conditions. However, as the cutterbar is moved fore or aft relative to its pivot or other point of support, the effect of the preload, e.g., ground following characteristics, can change also, which may be undesirable and negatively impact the harvesting and/or gathering operation. For instance, if the cutterbar is moved in the forward direction, the center of gravity thereof may be moved more distant from the pivot point, thus reducing the preload effect. Conversely, if the cutterbar is retracted, the effective preload may be increased.
What is sought therefore, is a header with a fore and aft adjustable flexible cutterbar, which provides a capability for automatically adjusting a preload force exerted against the cutterbar as a function of the fore and aft position thereof, and which overcomes one or more of the disadvantages and shortcomings, set forth above.